1. Technical Field
The present invention relates to a refrigerant compressor, and more particularly, to a slant plate type compressor such as a wobble plate compressor having a variable displacement mechanism suitable for use in an automotive air-conditioning system.
2. Description of the Prior Art
Slant plate type piston compressors provided with a displacement or capacity adjusting mechanism to control the compression ratio of the compressor in response to demand are known in the art. As disclosed in U.S. Pat. No. 3,861,829, the compression ratio may be controlled by changing the slant angle of the sloping surface of the slant plate in response to the operation of a valve control mechanism. The slant angle of the slant plate is adjusted in repsonse to a change in suction chamber pressure to restore the suction chamber pressure to a constant level.
The construction of a slant plate type compressor, specifically a wobble plate type refrigerant compressor in accordance with one embodiment of the prior art is shown in FIG. 1. Compressor 10 includes cylindrical housing assembly 20 further including cylinder block 21, front end plate 23 at one end of cylinder block 21, crank chamber 22 enclosed within cylinder block 21 by front end plate 23, and rear end plate 24 attached to the other end of cylinder block 21. Front end plate 23 is mounted on cylinder block 21 forward of crank chamber 22 (to the left in FIG. 1) by a plurality of bolts 101. Rear end plate 24 is mounted on cylinder block 21 at its rearward end by a plurality of bolts (not shown). Valve plate 25 is disposed between rear end plate 24 and cylinder block 21.
Bearing 30 is disposed within opening 231 centrally formed in front end plate 23. Bearing 30 supports drive shaft 26 within opening 231. Bearing 31 is disposed within central bore 210 formed in cylinder block 21. Bearing 31 rotatably supports the inner end portion of drive shaft 26 within central bore 210. Cavity 220 is formed in cylinder block 21 to the rear of and adjacent to bore 210. Valve control mechanism 19 is disposed within cavity 220. Hole 220a is formed in cylinder block 21 and links cavity 220 and bore 210.
Cam rotor 40 is fixed on drive shaft 26 by pin member 261 and rotates with drive shaft 26. Thrust needle bearing 32 is disposed between the inner end surface of front end plate 23 and the adjacent axial end surface of cam rotor 40. Cam rotor 40 includes arm 41 having pin member 42 extending therefrom. Sliding element 54 is disposed on drive shaft 26. Slant plate 50 includes opening 53 and is disposed adjacent to cam rotor 40. Slant plate 50 is disposed around sliding element 54 for movement thereabout to adjust the slant or incline angle of slant plate 50 with respect to a plane perpendicular to the longitudinal axis of drive shaft 26. Slant plate 50 includes arm 51 having slot 52. Cam rotor 40 and slant plate 50 are connected via pin member 42 inserted in slot 52 to create a hinged joint. Pin member 42 is slidable within slot 52 to allow adjustment of the slant angle of slant plate 50. Slant plate 50 rotates with cam rotor 40.
Wobble plate 60 is nutatably mounted on slant plate 50 through bearings 61 and 62. Sliding rod 64 is fixed between front end plate 23 and cylinder block 21. Slider 63 is attached to one peripheral end of wobble plate 60 and is slidably mounted on sliding rod 64, allowing wobble plate 60 to nutate along sliding rod 64 when cam rotor 40 rotates, but preventing rotation of wobble plate 60. Cylinder block 21 includes a plurality of pistons 71 located in a plurality of cylinder chambers 70. One piston 71 reciprocates in each cylinder chamber 70 and is connected to the peripheral end of wobble plate 60 by a corresponding connecting rod 72.
Rear end plate 24 includes centrally located discharge chamber 251 and peripheral annular suction chamber 241 located around discharge chamber 251. Valve plate 25 includes a plurality of valved suction ports 242 linking suction chamber 241 with a respective cylinder 70. Valve plate 25 also includes a plurality of valved discharge ports 252 linking discharge chamber 251 with a respective cylinder 70. Suction ports 242 and discharge ports 252 are provided with suitable reed valves (not shown) as described in U.S. Pat. No. 4,011,029 to Shimizu.
Rear end plate 24 includes inlet portion 241a linking suction chamber 241 with an evaporator of an external cooling circuit (not shown). Rear end plate 24 also includes outlet portion 251a linking discharge chamber 251 to a condenser of the cooling circuit (not shown). Gaskets 27 and 28 are disposed between cylinder block 21 and the inner surface of valve plate 25 and the outer surface of valve plate 25 and rear end plate 24, respectively. Gaskets 27 and 28 seal the mating surfaces of cylinder block 21, valve plate 25, and rear end plate 24.
With reference to FIG. 2, valve control mechanism 19 includes cup-shaped casing member 191 having end plate 193 attached at its open end. Valve chamber 192 is enclosed within cup-shaped casing 191 by end plate 193. O-ring 19a is disposed between the outer surface of casing member 191 and the inner surface of cavity 220 to seal the mating surfaces of casing member 191 and cylinder block 21. A plurality of holes 19b are formed through casing member 191 and link valve chamber 192 with suction chamber 241 through conduit 221 formed in cylinder block 21, and hole 222 formed through valve plate 25. Therefore, valve chamber 192 is maintained at the suction chamber pressure. Bore 19c is formed through the closed end of casing member 191 and links valve chamber 192 to crank chamber 22 through hole 220a, bore 210, and gap 31a between bearing 31 and cylinder block 21.
Bellows 194 is disposed in valve chamber 192 and longitudinally contracts or expands in response to the suction chamber pressure. Projection member 194b is attached to the rearward (rightside) end of bellows 194 and is secured within axial hole 193a formed through the center of end plate 193. Hemispherical valve member 194a is disposed at the forward end of bellows 194 and is moved into and out of a position sealing bore 19c in accordance with the expansion and contraction of bellows 194. Passageway 17 links crank chamber 22 and suction chamber 241, and includes gap 31a, bore 210, hole 220a, bore 19c, valve chamber 192, holes 19b, conduit 221, and hole 222. The opening and closing of passageway 17 is controlled by the contraction and expansion of bellows 194 in response to suction chamber pressure.
When the compressor is operated, drive shaft 26 is rotated by the engine of the vehicle through electromagnetic clutch 300. Cam rotor 40 rotates with drive shaft 26, rotating slant plate 50 as well, and causing wobble plate 60 to nutate. Nutational motion of wobble plate 60 reciprocates pistons 71 in their respective cylinders 70. As pistons 71 are reciprocated, refrigerant gas introduced into suction chamber 241 through inlet portion 241a flows into each cylinder 70 through suction ports 242 and is compressed in the cylinders. Compressed gas is discharged from cylinder 70 to discharge chamber 251 through discharge ports 252, and from discharge chamber 251 to the external cooling circuit through outlet portion 251a.
During operation of the compressor, the suction chamber pressure will change in response to a change in the heat load of the evaporator or to a change in the rotation speed of drive shaft 26. Additionally, the capacity of compressor 10 is dependent upon the slant angle of slant plate 50 and wobble plate 60. When the pressure in crank chamber 22 increases, the slant angle of the slant plate and the wobble plate decreases, thereby decreasing the capacity of the compressor. When the crank chamber pressure decreases, the slant angle increases, and the capacity of the compressor is increased.
Valve control mechanism 19 functions to maintain a predetermined suction chamber pressure in response to changes in the suction chamber pressure, that is, valve control mechanism 19 functions to restore the suction chamber pressure to a predetermined value when it changes. Since valve control mechanism 19 controls the link between the crank chamber and the suction chamber through passageway 17, valve control mechanism 19 controls the pressure within the crank chamber and thus functions to control the slant angle of the wobble plate and the slant plate to control the capacity of the compressor.
Valve control mechanism 19 functions in the following manner. When the suction chamber pressure exceeds a predetermined value due to an increase in the heat load of the evaporator or a decrease in the rotational speed of the compressor, bellows 194 contracts, moving hemispherical valve member 194a to the right in FIG. 2 and opening bore 19c. Crank chamber 22 is linked to suction chamber 241 causing the pressure in the crank chamber to decrease to the pressure in the suction chamber. The slant angle of slant plate 50 and wobble plate 60 is at a maximum value, and thus the capacity of compressor 10 is also maximized.
If the suction chamber pressure decreases below the predetermined value due to a decrease in the heat load of the evaporator or to an increase in the rotational speed of the compressor, bellows 194 expands, moving hemispherical valve member 194a to the left, closing bore 19c. The link between crank chamber 22 and suction chamber 241 is terminated and the pressure in crank chamber 22 gradually increases due to blow-by gas, that is, compressed refrigerant gas in cylinder chamber 70 bypassing a gap between piston 71 and the surface of cylinder chamber 70. Accordingly, the slant angle of slant plate 50 and wobble plate 60 gradually decreases, and the capacity of compressor 10 is gradually decreased as well.
However, if during operation the heat load of the evaporator is extremely large (for example when the compressor begins to operate on a hot day), the rotational speed of the compressor will be simultaneously high, and the suction pressure will be quickly reduced to below the predetermined value. Therefore, bellows 194 expands, terminating the link between the suction chamber and the crank chamber. The crank chamber pressure increases, reducing compressor displacement well before the passenger compartment temperature of the automobile is reduced sufficiently.